Before you go changing out all your tubing do a flow rate test. Get a couple of 5 gallon buckets and fill one up with a gallon measuring jug and mark gallon increments.
Time how long it takes to move 3 gallons of water through your system.
Most people will average around 1.5 gallons per minute with an average 1/2 loop system. Folks running really high wattage pumps or dual pumps or CPU only loops etc can see 2 gal/min or I've even heard 3 gal/min.
Now take a look at the Fuzion thermal performance:
Assuming your rads/fans are up to the job, this gives you an idea of how the performance is impacted by flow rate. You'll loose out on quite a bit of performance if you're flowing less than a gallon per minute, but I'm sure it would still be an improvement and if nothing else at least a step in the direction of improving the system, maybe make some more upgrades later.